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WO2005045815A1 - Transducteurs optiques a champ proche pour stocker des donnees optiques et magnetiques assiste thermiquement - Google Patents

Transducteurs optiques a champ proche pour stocker des donnees optiques et magnetiques assiste thermiquement Download PDF

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Publication number
WO2005045815A1
WO2005045815A1 PCT/US2003/032324 US0332324W WO2005045815A1 WO 2005045815 A1 WO2005045815 A1 WO 2005045815A1 US 0332324 W US0332324 W US 0332324W WO 2005045815 A1 WO2005045815 A1 WO 2005045815A1
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WO
WIPO (PCT)
Prior art keywords
pin
electromagnetic wave
optical transducer
optical
directing
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/US2003/032324
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English (en)
Inventor
Chubing Peng
William A. Challener
Ibrahim K. Sendur
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Seagate Technology LLC
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Seagate Technology LLC
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Filing date
Publication date
Application filed by Seagate Technology LLC filed Critical Seagate Technology LLC
Priority to AU2003284100A priority Critical patent/AU2003284100A1/en
Priority to PCT/US2003/032324 priority patent/WO2005045815A1/fr
Publication of WO2005045815A1 publication Critical patent/WO2005045815A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/127—Structure or manufacture of heads, e.g. inductive
    • G11B5/31—Structure or manufacture of heads, e.g. inductive using thin films
    • G11B5/3109—Details
    • G11B5/313—Disposition of layers
    • G11B5/3133—Disposition of layers including layers not usually being a part of the electromagnetic transducer structure and providing additional features, e.g. for improving heat radiation, reduction of power dissipation, adaptations for measurement or indication of gap depth or other properties of the structure
    • G11B5/314—Disposition of layers including layers not usually being a part of the electromagnetic transducer structure and providing additional features, e.g. for improving heat radiation, reduction of power dissipation, adaptations for measurement or indication of gap depth or other properties of the structure where the layers are extra layers normally not provided in the transducing structure, e.g. optical layers
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/02—Recording, reproducing, or erasing methods; Read, write or erase circuits therefor
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1387—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector using the near-field effect
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
    • G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
    • G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
    • G11B11/10532—Heads
    • G11B11/10534—Heads for recording by magnetising, demagnetising or transfer of magnetisation, by radiation, e.g. for thermomagnetic recording
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B2005/0002—Special dispositions or recording techniques
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B2005/0002—Special dispositions or recording techniques
    • G11B2005/0005—Arrangements, methods or circuits
    • G11B2005/0021—Thermally assisted recording using an auxiliary energy source for heating the recording layer locally to assist the magnetization reversal

Definitions

  • This invention relates to optical transducers, and more particularly to optical transducers that can be used in optical recording and thermally assisted magnetic recording.
  • BACKGROUND OF THE INVENTION [0002]
  • thermally assisted optical/magnetic data storage information bits are recorded on a layer of a storage medium at elevated temperatures, and the heated area in the storage medium determines the data bit dimension.
  • an electromagnetic wave in the form of light is used to heat the storage medium.
  • Heat assisted magnetic recording generally refers to the concept of locally heating a recording medium to reduce the coercivity of the recording medium so that the applied magnetic writing field can more easily direct the magnetization of the recording medium during the temporary magnetic softening of the recording medium caused by the heat source.
  • Heat assisted magnetic recording allows for the use of small grain media, which is desirable for recording at increased areal densities, with a larger magnetic anisotropy at room temperature to assure sufficient thermal stability.
  • Heat assisted magnetic recording can be applied to any type of magnetic storage media, including tilted media, longitudinal media, perpendicular media and patterned media.
  • Heat assisted magnetic recording requires an efficient technique for delivering large amounts of light power to the recording medium confined to spots of, for example, 50 nm or less.
  • Solid immersion lenses SILs
  • solid immersion mirrors SIMs
  • the optical intensity is very high at the focus but the spot size is still determined by the diffraction limit which in turn depends on the refractive index of the material from which the SIL or SIM is made.
  • the smallest spot size which can be achieved with all currently known transparent materials is ⁇ 60 nm, which is too large for HAMR.
  • a metal pin can be used as a transducer to concentrate optical energy into arbitrarily small areal dimensions.
  • the pin supports a surface plasmon mode which propagates along the pin, and the width of the external electric field generated by the surface plasmon mode is proportional to the diameter of the pin.
  • An optical transducer comprises means for directing an electromagnetic wave to a focal region and a metallic nano-structure having a longitudinal axis substantially parallel to an electric field of the electromagnetic wave, the metallic nano-structure being positioned outside of the means for directing an electromagnetic wave, wherein the electromagnetic wave produces surface plasmons on the metallic nano-structure.
  • the invention also encompasses an optical transducer comprising means for directing an electromagnetic wave to a focal region, the means for directing an electromagnetic wave having a first index of refraction, a metallic nano-structure positioned at the focal region, and a cladding material having a second refractive index positioned adjacent to a surface of the metallic nano-structure.
  • FIG. 1 is a pictorial representation of a magnetic disc drive that can include magnetic heads constructed in accordance with this invention.
  • FIG. 2 is a schematic representation of a transducer constructed in accordance with this invention.
  • FIGs. 3a and 3b are side elevation views of metallic nano-structures that can be used in the transducers of this invention.
  • FIGs. 4, 5, 6 and 7 are graphs of data illustrating simulated performance of the transducers of this invention.
  • FIG. 8 is a side view of a portion of a patterned data storage medium that can be used in combination with the transducers of this invention.
  • FIG. 9 is a top plan view of the data storage medium of FIG. 8.
  • FIGs. 10, 11, 12 and 13 are graphs of data illustrating simulated performance of the transducers of this invention.
  • FIGs. 14, 15, 16, 17, 18 and 19 are schematic representations of transducers constructed in accordance with this invention.
  • FIG. 20, 21 and 22 are isometric views of various lens structures that can be used in the transducers of this invention.
  • FIGs. 23, 24 and 25 are schematic representations of transducers used to illustrate the operation of the transducers of this invention.
  • FIG. 26 is a graph of data illustrating simulated performance of the transducers of this invention.
  • FIGs. 27 and 28 are schematic representations of transducers used to illustrate the operation of the transducers of this invention.
  • FIG. 29 is a side view of a pin used in the transducers of FIGs. 27 and 28.
  • FIG. 30 is a graph of data illustrating simulated performance of the transducers of this invention.
  • FIGs. 31 and 32 are schematic representations of transducers used to illustrate the operation of the transducers of this invention.
  • FIGs. 33 and 34 are a schematic representations of portions of transducers constructed in accordance with the invention.
  • FIG. 35 is a graph of data illustrating simulated performance of the transducers of FIGs. 33 and 34.
  • FIGs. 36 through 43 are schematic representations of portions of transducers constructed in accordance with the invention.
  • FIG. 44 is a graph of the normalized power distribution for two sensor configurations.
  • FIGs. 45 and 46 are graphs showing the effect of dielectric thickness in the transducers.
  • FIG. 47 is a schematic representation of a magneto-optic recording head constructed in accordance with this invention.
  • DETAILED DESCRIPTION OF THE INVENTION This invention encompasses transducers that can be used in magnetic and optical recording heads for use with magnetic and/or optical recording media, as well as magnetic and/or optical recording heads that include such devices and disc drives that include the recording heads.
  • FIG. 1 is a pictorial representation of a disc drive 10 that can utilize recording heads constructed in accordance with this invention.
  • the disc drive includes a housing 12 (with the upper portion removed and the lower portion visible in this view) sized and configured to contain the various components of the disc drive.
  • the disc drive includes a spindle motor 14 for rotating at least one data storage medium 16 within the housing, in this case a magnetic disc.
  • At least one arm 18 is contained within the housing 12, with each arm 18 having a first end 20 with a recording and/or reading head or slider 22, and a second end 24 pivotally mounted on a shaft by a bearing 26.
  • An actuator motor 28 is located at the arm's second end 24, for pivoting the arm 18 to position the head 22 over a desired sector of the disc 16.
  • the actuator motor 28 is regulated by a controller that is not shown in this view and is well-known in the art.
  • an electromagnetic wave of, for example visible, infrared or ultraviolet light is directed onto a surface of a data storage medium to raise the temperature of a localized area of the medium to facilitate switching of the magnetization of the area.
  • Well-known solid immersion lenses (SILs) have been proposed for use in reducing the size of a spot on the medium that is subjected to the electromagnetic radiation.
  • solid immersion mirrors (SIMs) have been described in the literature and proposed for use in heat assisted magnetic recording heads. SILs and SIMs may be either 3 -dimensional or 2-dimensional.
  • Planar waveguides that include focusing means such as mode index lenses and mirrors can also be used to concentrate the electromagnetic wave.
  • All of these structures can serve as means for concentrating an electromagnetic wave to a focal region.
  • a nano-structure such as a metallic pin, can be positioned near the focal region to guide the electromagnetic wave to the surface of a recording medium.
  • This invention provides an efficient means of coupling an electromagnetic wave to a nano-structure, such as a metallic pin.
  • FIG. 2 is a schematic representation of a transducer 30 constructed in accordance with this invention.
  • a source of electromagnetic radiation such as a laser 32 produces a radially polarized beam of light illustrated by arrows 34 and 36 that is delivered to an objective lens 38.
  • a solid hemispheric lens 40 receives the light and concentrates it to a focal region 42.
  • a nano-structure 44 in the form of an elongated metallic nano-wire, also called a pin, is positioned near the focal region. The light, having unit power over the lens aperture, is brought to focus onto the center of the hemisphere by the objective lens, and illuminates the metallic pin.
  • a magnetic storage medium 46 including a storage layer 48, which can be a 12 nm thick layer of a cobalt alloy or multilayer of cobalt and/or iron, a heat-sink layer 50, which can be a 100 nm thick gold layer, and a substrate 52, is placed below the transducer.
  • One end of the transducer can be separated from the surface of the storage medium by an air gap of, for example, 10 nm.
  • the numerical aperture of the objective lens is 0.85
  • the refractive index of the solid hemisphere is 2.09.
  • the end of the nano-structure is separated from the solid hemispheric lens 40 by a gap 56.
  • the length of gap 56 should be less than 50 nm.
  • X, Y, Z are three axes of a right-handed Cartesian coordinate system.
  • the origin of the coordinate system (x, y, z) (0,0,0) is at the center of the bottom surface of the solid hemisphere, which is also the focal point.
  • the operation of the transducer has been simulated for transducers wherein the nano-structure comprises a gold pin or a silver pin.
  • FIG. 3 a shows a pin 44 having a longitudinal axis 60 and a square cross-sectional shape in a plane perpendicular to the longitudinal axis.
  • FIG. 3b shows a pin 62 having a longitudinal axis 64, a square cross- sectional shape in a plane perpendicular to the longitudinal axis, and a tapered end 66.
  • the complex refractive index is 0.188 + j 5.89 for the gold pin, and the complex refractive index is 2.53 + j 4.88 for the storage medium, which is similar to cobalt.
  • line 68 represents data for the flat end pin and dots 70 represent data for the pointed end pin.
  • displayed in FIG. 4 has been multiplied by the light wavelength. It is evident that the magnitude of
  • I E y Compared to the E-field at the center of the focal- plane in the absence of the pin and storage medium, I E y
  • the cross-sectional E-field distribution at a distance of 7.5 nm below the pin has been calculated for a gold pin 48 nm x 48 nm x 100 nm long with a flat end and for a gold pin 48 nm x 48 nm x 374 nm long with a pointed end.
  • the FWHM spot size is 23 nm.
  • the E-field near the tip of the pin in the XY plane is enhanced and confined.
  • Solid lines 80 and 82 represent the field strength with a gold pin, which are evaluated at 2.5 nm below the gold pin, while the dashed lines 84 and 86 represent the fields at the focal-plane when the metal pin and storage media are absent.
  • the gold pin dimensions were 48 nm x 48 nm x 374 nm.
  • the peak temperature rise (AT) at the surface of the storage layer illuminated by the laser has been calculated for 2 ns illumination duration.
  • FIG. 7 shows the calculated peak temperature rise at the surface of the storage layer under illumination of a 10 mW laser output for 2 ns duration of illumination as a function of gold pin length for a flat-end pin, illustrated by line 90, and for a pointed-end pin, illustrated by dots 92. In the calculation it was assumed that the storage layer was homogeneous and continuous and that the substrate was flat.
  • the storage layer 102 is comprised of granular islands 104, separated by a dielectric material 106, for instance, free-space. Each granule has a size (a x a) in the XZ plane. The separation between granules is a distance b.
  • the storage layer is positioned on a heat sink 108, which is positioned on a substrate 110.
  • FIG. 10 shows the calculated
  • at (x, z) (0, 0) and 7.5 nm below the end of the pin as a function of pin length. It is evident that the magnitude of I E y I varies with pin length.
  • the silver pin reaches resonance and the I E y I magnitude is maximized.
  • the E-field strength with a pin length of 300 nm is much weaker than that with a pin length of 96 nm, differing from the case of the gold pin, due to the different pin size.
  • the E-field is enhanced by a factor of 16.
  • the solid lines 112 and 114 represent the field strength with a silver pin and storage medium, which were evaluated at 2.5 nm below the silver pin, while the dashed lines 116 and 118 represent the fields at the focal plane without the metal pin or storage medium.
  • the silver pin was assumed to have dimensions of 25 nm x 25 nm x 96 nm, with both ends being flat.
  • the E-field strength with the pin is -330 times stronger than that without a pin and the maximum E-field does not occur at the center of the pin.
  • FIG. 13 shows the calculated peak temperature rise (AT) at the surface of the continuous storage layer under illumination of a laser for 2 ns as a function of silver pin length.
  • the optical power input to the transducer is 10 mW. In the calculation it was assumed that the storage layer is homogeneous and continuous and that the substrate is flat.
  • FIGs. 14, 15 and 16 are schematic representations of transducers in accordance with other implementations of the present invention.
  • a radially polarized beam of light 130 is brought to focus on an elongated metallic pin 134 with a 3-dimensional rotational paraboloid mirror 132.
  • Pin 134 is located at the center of focal- plane and extends below the paraboloid mirror.
  • FIG. 15 a radially polarized beam of light 136 is brought to focus on an elongated metallic pin 138 using a rotational ellipsoid/paraboloid 140 embedded in a medium 142 that has lower refractive index.
  • FIG. 16 shows a pin 144 positioned at the end of a solid immersion mirror (SIM) 146.
  • SIM solid immersion mirror
  • FIGs. 17, 18 and 19 are schematic representations of a transducer in accordance with additional implementations of the present invention.
  • FIG. 17 is an end view of a transducer 150
  • FIG. 18 is a side view of the transducer of FIG. 17.
  • the transducer 150 includes a 2-dimensional waveguide SEVI 152 and a metallic pin 154.
  • Light is coupled into one transverse electric (TE) mode of the thin-film planar waveguide with two gratings 156 and 158 that are shifted to yield a ⁇ phase difference between the light beams coupled into the waveguide.
  • the waveguide core layer 160 has a higher refractive index than that of the surrounding medium 162 and also that of the cladding layer 164.
  • FIG. 19 is a side view of another example of the transducer 170 in which the waveguide 172 has a different thickness near the pin 174.
  • FIGs. 20, 21 and 22 are isometric views of micro-lens structures that can be used in the transducers of this invention.
  • the transducer 180 comprises a 2- dimensional waveguide 182, a geodesic lens 184, and a metallic pin 186.
  • FIG. 20 the transducer 180 comprises a 2- dimensional waveguide 182, a geodesic lens 184, and a metallic pin 186.
  • the transducer 188 comprises a 2-dimensional waveguide 190, a mode index lens 192, and a metallic pin 194.
  • the transducer 196 comprises a 2-dimensional waveguide 198, a diffractive lens 200, and a metallic pin 202.
  • the light is condensed to illuminate an elongated metallic pin with the micro-lens.
  • Dual gratings or other means of launching a dual light beam into the waveguide with a relative ⁇ phase shift can be used for ensuring a polarization at the focal point for which the electric field is directed along the axis of the pin.
  • the pin is positioned outside of the focusing/condensing means.
  • Three examples are illustrated in FIGs 23, 24 and 25 to demonstrate the superiority of the present invention compared to previously proposed "pin inside" transducers.
  • the examples of FIGs. 23, 24 and 25 each include an objective lens 210, 212 and 214 and a solid hemisphere or cap 216, 218 and 220.
  • a silver pin 222 is placed inside the hemisphere in FIG. 23.
  • a silver pin 224 is located outside the cap in FIG. 24.
  • a silver pin 226 is located outside the hemisphere in FIG. 25.
  • FIG. 26 shows the calculated E y versus pin length for the transducers of FIGs. 23, 24 and 25.
  • a radially polarized beam of light is focused by an objective lens onto the bottom plane of a solid hemisphere/cap.
  • the focusing lens has a numerical aperture of 0.85, and the hemisphere/cap has a refractive index of 2.09.
  • the wavelength is 830 nm.
  • the E-field is evaluated at 7.5-nm below the pin.
  • the magnitude of E y displayed has been multiplied by the light wavelength.
  • the cap is a truncated solid immersion lens. Its width is less than the radius of the hemisphere.
  • a storage medium 228 is positioned 10 nm away from the pin.
  • the storage medium includes a 12 nm cobalt storage layer 230, a 100 nm gold heat-sink layer 232, and a substrate 234.
  • FIGs. 24 and 25 are referred to as "pin outside" transducers.
  • the silver pin in these examples has a cross-section of 25 nm by 25 nm.
  • the pin length is optimized to yield maximum electric field strength in each configuration.
  • FIG. 26 displays the calculated results as a function of pin length.
  • Curve 240 corresponds to the "pin inside" configuration of FIG.
  • curves 242 and 244 correspond to the "pin outside" configuration of FIGs. 24 and 25. It is seen that the electric field varies with pin length for the three cases studied. The difference is that, in the "pin inside” configuration, the dependence of electric field on the pin length is weak, while it is pronounced in the "pin outside” configurations. The electric field is maximized at a pin length of 35 nm for the pin inside the hemisphere, at a pin length of 72 nm for the pin outside the cap, and at a pin length of 80-100 nm for a pin outside the hemisphere. Resonance is reached at a longer pin when the pin is placed outside of the SIL.
  • the I E 1 2 electric field intensity with the pin outside the SIL is ⁇ 16 times greater than with the pin inside the SIL. Having a longer resonant pin length or a higher aspect ratio of the silver pin generates a higher electric field near the end of the pin.
  • FIGs. 27 and 28 show various transducer configurations used for simulation calculations.
  • FIG. 29 shows the pin used in the transducers of FIGs. 27 and 28.
  • a radially polarized beam of light is focused by an objective lens 250, 252 onto the bottom plane of a solid hemisphere 254, 256.
  • the focusing lens 250, 252 has a numerical aperture of 0.85, and the hemisphere 254, 256 has a refractive index of 2.09.
  • the wavelength is 830 nm.
  • a gold pin 258, 260 is placed inside the hemisphere in FIG. 27, or outside the hemisphere in FIG. 28.
  • a storage medium 260, 262 is positioned 10 nm away from the pin.
  • FIG. 30 is a graph of the magnitude of y-component of electric field versus gold pin length for a pin inside the hemisphere and a pin outside the hemisphere. The field is evaluated at 7.5 nm below the pin. The magnitude of displayed E y has been multiplied by the light wavelength.
  • FIG. 30 plots the calculated results as a function of pin length.
  • Curve 270 corresponds to the "pin inside” configuration of FIG. 27, while curve 272 corresponds to the "pin outside” configuration of FIG. 28. It is seen that, with the pin outside the hemisphere, the electric field varies strongly with pin length. The electric field peaks at a pin length of 70 nm for the pin inside the hemisphere, and at a pin length of 134 nm for the pin outside the hemisphere. At the optimized pin length, the electric field strength with the pin outside is ⁇ 3 times greater than that with the inside pin. A higher aspect ratio of the pin at resonance for the outside pin causes a higher electric field near the end of the pin.
  • FIGs. 31 A, 3 IB, 32A and 32B show transducer configurations for the pin inside the SIL and the pin outside the SIL. Similar to FIGs. 24, 25 and 26, a radially polarized beam of light is focused by an objective lens 280, 282 onto the bottom plane of a solid hemisphere 284, 286.
  • the focusing lens 280, 282 has a numerical aperture of 0.85, and the hemisphere has a refractive index of 2.09. The wavelength is 830 nm.
  • a gold pin 288, 290 is placed inside the hemisphere in FIG. 31 A, or outside the hemisphere in FIG. 32A.
  • a storage medium 292, 294 is positioned 10 nm below the pin.
  • the gold pin 288 inside the hemisphere, as shown in the FIG. 3 IB, is an inverted pyramid, while the pin 290 of FIG. 32B outside the hemisphere is an elongated cube with a pointed tip.
  • this invention encompasses additional plasmon enhancing pin-stack configurations to improve the transmission efficiencies of the optical transducers.
  • a layer of material having a refractive index that differs from the refractive index of the surrounding material is used to increase transmission efficiency.
  • FIG. 33 is a schematic representation of a portion of a transducer 300 that includes a metallic pin 302 and layers 304 and 306 of a high index dielectric material positioned on opposite sides of the pin.
  • Electromagnetic waves 308 and 310 which are 180° out of phase with each other are directed onto the pin to create surface plasmon modes on the surfaces of the pin. This concentrates the electric field at the end 312 of the pin to heat a data storage medium 314.
  • the data storage medium includes a magnetic recording layer 316, a heat sink layer 318 and a substrate 320.
  • the pin 302 and layers 304 and 306 are positioned in air, and the refractive index of the layers 304 and 306 is greater than that of air.
  • This structure will be referred to as LHM (low index dielectric - high index dielectric - metallic pin) structure.
  • FIG. 34 is schematic representation of a portion of a transducer 330 that includes a metallic pin 332 and layers 334 and 336 of a low index dielectric material positioned on opposite sides of the pin. Electromagnetic waves 338 and 340 which are 180° out of phase with each other are directed onto the pin to create surface plasmon modes on the surfaces of the pin. This concentrates the electric field at the end 342 of the pin to heat a data storage medium 344.
  • the data storage medium includes a magnetic recording layer 346, a heat sink layer 348 and a substrate 350.
  • the pin 332 and layers 334 and 336 are positioned in high dielectric material waveguide 352, and the refractive index of the layers 334 and 336 is less than that of the waveguide 352.
  • This structure will be referred to as HLM (high index dielectric - low index dielectric - metallic pin) structure.
  • FIG. 35 is a graph of the dissipated power density on the top surface of the storage medium for the structures of FIGs. 33 and 34.
  • line 366 represents the dissipated power in the surface of the medium for a pin embedded in a high index waveguide, without any cladding material.
  • Line 364 represents the dissipated power in the surface of the media for a pin placed at the focus of a lens system.
  • Line 360 represents the dissipated power in the surface of the media for a HLM structure.
  • Line 362 represents the dissipated power in the surface of the media for a LHM structure.
  • the data in FIG. 35 suggests that the configurations of FIGs. 33 and 34 improve transmission efficiencies.
  • the pins and surrounding structures of FIGs. 33 and 34 assumed cylindrical pins.
  • rectangular pins may be more appropriate.
  • the surrounding dielectrics can be either rectangular prisms or planar surfaces.
  • the later configurations can accommodate magnetic recording poles in a heat assisted magnetic recording system.
  • a more complex multilayer structure such as the one in FIG. 36 can be used.
  • a multilayer structure 370 can be embedded in a low or high refractive index material 372.
  • the multilayer structure can be viewed in two ways. If used in a cylindrically symmetric optical system, such as a SIL, the layers can be half concentric cylindrical layers. Alternatively, the layers can be planar surfaces with different optical properties.
  • the multilayer structure 370 includes a pin 374 and several layers 376, 378, 380 and 382 positioned on opposite sides of the pin as shown in FIG. 36.
  • Linearly polarized or radially polarized light as indicated by arrows 384 and 386 is directed to illuminate the multilayer structure to create surface plasmons on the pin.
  • An air bearing surface 388 of the transducer is positioned adjacent to a storage medium 390.
  • the storage medium includes a cobalt recording layer 392, a heat sink layer 394 and a substrate 396.
  • the air bearing surface of the transducer is separated from the storage medium by a gap 398.
  • the width and length of the pin and the dielectric materials can be adjusted for optimum performance.
  • the electrical properties of the dielectric materials can be optimized.
  • the metal used for the pin can be selected to enhance excitation of surface plasmons.
  • the metallic pin is covered on the sides only.
  • the pin can be embedded in the dielectric material as shown in FIG. 37.
  • the transducer 400 of FIG. 37 includes a metallic pin 402 and layers 404 and 406 of a low index dielectric material positioned on opposite sides of the pin.
  • An additional layer 408 of dielectric material is positioned at the end of the pin.
  • Electromagnetic waves 410 and 412 which are 180° out of phase with each other are directed onto the pin to create surface plasmons modes on the surfaces of the pin. This concentrates the electric field at the end 414 of the pin to heat a data storage medium 416.
  • the data storage medium includes a magnetic recording layer 418, a heat sink layer 420 and a substrate 422.
  • the pin 402 and layers 404, 406 and 408 are positioned in a dielectric material waveguide 424 having a high refractive index, and the refractive index of the layers 404, 406 and 408 is less than that of the waveguide 424.
  • FIG. 38 illustrates a transducer 430 that includes a conical pin structure.
  • a conical pin 432 is surrounded by a dielectric cladding material 434 having a low index of refraction.
  • the pin structure is embedded in a high index dielectric material 436.
  • Radially polarized light indicated by arrows 438 and 440 is directed onto the sides of the pin structure to excite plasmons on the surface of the pin.
  • An end 442 of the pin is positioned adjacent to the storage medium 444, and separated from the storage medium by a gap 446.
  • FIGs. 39 and 40 are front and side views of a transducer 450 that includes a planar triangular pin structure.
  • a planar triangular pin 452 is positioned between dielectric cladding layers 454, 456, 474 and 476 having a low index of refraction.
  • the pin structure is embedded in a high index dielectric material 458.
  • Radially polarized light indicated by arrows 460, 462, 464 and 466 is directed onto the sides of the pin structure to excite plasmons on the surface of the pin.
  • An end 468 of the pin is positioned adjacent to the storage medium 470, and separated from the storage medium by a gap 472.
  • FIG. 41 illustrates a transducer 480 that includes an elliptical pin structure.
  • an elliptical pin 482 is surrounded by a dielectric cladding material 484 having a low index of refraction.
  • the pin structure is embedded in a high index dielectric material 486.
  • Radially polarized light indicated by arrows 488 and 490 is directed onto the sides of the pin structure to excite plasmons on the surface of the pin.
  • An end 492 of the pin is positioned adjacent to the storage medium 494, and separated from the storage medium by a gap 496.
  • FIG. 42 is a schematic representation of a transducer 500 having a metallic pin 502 embedded in a solid immersion lens 504.
  • a low index dielectric cladding 506 surrounds the pin.
  • the solid immersion lens serves as a means for directing radially polarized light onto the pin.
  • FIG. 43 is a schematic representation of a transducer 510 having a metallic pin 512 embedded in a planar waveguide 514.
  • a low index dielectric cladding 516 surrounds the pin.
  • Gratings 518 and 520 serve to couple light into the waveguide.
  • the gratings are offset to produce split linearly polarized light in the waveguide.
  • the planar waveguide lens serves as a means for directing split linearly polarized light onto the pin.
  • rectangular prism-shaped pin structures may be preferred for some applications such as heat-assisted magnetic recording.
  • different thicknesses and materials for the dielectrics can be used to improve the performance of the optical transducer in the vicinity of the magnetic recording pole.
  • Magnetic structures can be elongated in one direction and coated with dielectrics to improve transmission efficiencies.
  • the transducers of this invention increase transmission efficiencies.
  • the structures increase transmission efficiency by enhancing plasmon modes on the metallic pin. Therefore, the FWHM spot size is determined by the radius of the metallic pin, not by the thickness and index of the adjacent dielectrics. To illustrate this point, normalized power distributions are illustrated in FIG. 44. The data suggests that the FWHM spot size remains the same for these configurations. Minor fluctuations in the plots are due to the different discretizations used by the finite element modeling technique.
  • the thickness of the layers is among the parameters that need to be optimized for enhanced performance.
  • FIGs. 45 and 46 show the performance as a function of thickness.
  • FIG. 45 represents data for a gold pin with SiO 2 dielectric cladding in air. For this configuration, the optimum dielectric thickness was computed as 6 nm.
  • FIG. 46 represents data for a gold pin with an air dielectric layer mounted in a SiO 2 material. For this configuration, the optimum dielectric thickness was computed as 14 nm.
  • the various illustrated pinstack structures can be integrated with the previous optical transducers to improve the efficiencies without affecting the FWHM sizes.
  • the pin-stack structures are efficient configurations to couple the electromagnetic (EM) fields into the metal pin.
  • the pin-stack structures can be seen as analogous to Kretschmann and Otto surface plasmon launching techniques for infinite planar surfaces. Total internal reflection phenomena and high index-low index boundaries can be utilized to create evanescent waves around the boundaries, which increases the transmission efficiency due to surface plasmon enhancement. Better matching of the surface impedance can be another possible contributor to the enhanced transmission.
  • wave impedance of the surface plasmon modes are changing, hence resulting in a better match to the incident EM wave.
  • This invention provides a near-field optical transducer that includes an optical element for condensing an electromagnetic wave to a focal region, and an elongated metallic nano-structure.
  • the nano-structure can be positioned in the region directly adjacent to but outside of the focal plane created by the condensing element.
  • the long axis of the nano-structure is parallel to the direction of light propagation.
  • the source of light is focused onto a region near one end of the nano- structure by the optical element.
  • the focused beam for illuminating the nano-structure has a mode profile such that its electric field is substantially parallel to the long axis of the nano-structure.
  • the transducer confines the light and enhances the electric field at the other end of the nano-structure.
  • the transducer is brought in a close proximity to the storage layer.
  • the transducer differs from the prior systems in that the metallic nano-structure is outside of the condenser in a lower index medium rather than embedded in a high index dielectric material or in a focusing optical element. This yields improved electric field enhancement and can deliver large amount of optical power to patterned storage media.
  • the invention provides transducers including means for directing an electromagnetic wave onto a metallic pin, with one or more dielectric cladding layers positioned adjacent to the pin.
  • the cladding layers have an index of refraction that differs from the index of refraction of the surrounding material. This increases the amount of energy that can be delivered to a storage medium from the end of the pin.
  • the waveguide can be made of, for example, a high index dielectric core material like TiO 2 , Ta 2 O 5 , Si, SiN, or ZnS depending on the wavelength and refractive index desired.
  • a high index dielectric core material like TiO 2 , Ta 2 O 5 , Si, SiN, or ZnS depending on the wavelength and refractive index desired.
  • Si has a very large index of 3.5 at a wavelength of 1550 nm in the near infrared, but it is not transparent to visible light.
  • Ta O 5 has a lower index of about 2.1, but is transparent throughout the near infrared and visible.
  • the waveguide also contains dielectric cladding layers on either side of the core.
  • the cladding layer must have a lower refractive index than the core layer.
  • the difference in refractive index between the core and cladding should be as large as possible.
  • Air is a suitable dielectric for one side of the cladding.
  • Other dielectrics that could be used as cladding layers include SiO 2 with an index of 1.5 and Al 2 O 3 with an index of about 1.8.
  • TE transverse electric
  • means can be provided to phase shift a portion of the electromagnetic wave. This phase shift can be achieved by providing a means for launching the 2-dimensional analog of a radially polarized wave into the planar waveguide. This is referred to above as a split linear polarization waveguide mode.
  • this invention encompasses magnetic recording heads that include the above described transducers. FIG.
  • the recording head 550 may include a writer section comprising a main write pole 554 and a return or opposing pole 556 that are magnetically coupled by a yoke or pedestal 558.
  • the recording head 550 may be constructed with a write pole 554 only and no return pole 556 or yoke 558.
  • a magnetization coil 560 surrounds the yoke or pedestal 558 for energizing the recording head 550.
  • the recording head 550 also may include a read head, not shown, which may be any conventional type read head as is generally known in the art.
  • the waveguide can alternatively be positioned on the other side of the pole.
  • the pin and the pole can be the same material, in which case the pin can function as both the electromagnetic transducer and the source of the field.
  • the recording medium 552 is positioned adjacent to or under the recording head 550.
  • the recording medium 552 includes a substrate 562, which may be made of any suitable material such as ceramic glass or amorphous glass.
  • a heat sink layer and/or a soft magnetic underlayer 564 may be deposited on the substrate 562.
  • the soft magnetic underlayer 564 may be made of any suitable material such as, for example, alloys or multilayers having Co, Fe, Ni, Pd, Pt or Ru.
  • the heat sink layer may be made of any suitable layer such as Au, Ag, Cu or Al.
  • a hard magnetic recording layer 566 is deposited on the soft underlayer 564, with substantially perpendicular oriented magnetic domains contained in the hard layer 566. Suitable hard magnetic materials for the hard magnetic recording layer 566 may include at least one material selected from, for example, FePt or CoCrPt alloys having a relatively high anisotropy at ambient temperature.
  • the recording head 550 also includes a planar waveguide 568 that directs light received from a light source onto a surface of a recording medium to heat the magnetic recording medium 552 proximate to where the write pole 554 applies the magnetic write field H to the recording medium 552.
  • the planar waveguide includes a light transmitting layer 570.
  • the optical waveguide 568 acts in association with a light source 572 which transmits light, for example via an optical fiber 574, that is coupled to the optical waveguide 568, by a coupling means such as a grating 576.
  • the light source 572 may be, for example, a laser diode, or other suitable laser light sources.
  • EM radiation is transmitted from a pin 582 for heating the recording medium 552, and particularly for heating a localized area 584 of the recording layer 566.
  • the transducer is used to heat a portion of the storage medium and the heated portion of the storage medium is subjected to a magnetic field to affect the magnetization of a storage layer in the storage medium.
  • the magneto-optical recording head can also include a reader as is well-known in the art.
  • the optical waveguide 568 can be constructed in accordance with any of the waveguides described above.
  • the waveguides of this invention can also be used in optical recording applications in which either a magnetic field is not needed, such as write once and phase change recording, or where an external magnet could be positioned below the substrate, such as in magneto-optic recording.
  • these structures could potentially be useful in a probe storage application or for high resolution near field optical lithography or for high resolution near field microscopy.
  • the transducers of this invention utilize pins which are dimensioned such that plasmon modes at the pins result from collective oscillations of electrons. This is also referred to as dipole plasmon resonance of the pins.
  • the pin structures described in the examples have dimensions of a few hundred nanometers or less. Therefore, they can be described as nanoparticles or nano-structures. This resonance includes the geometric effects due to the shape and size of the pins. It is generally desirable for the metallic pins to have an aspect ratio (length to width) of 2:1 or greater. However, optimization of the aspect ratio of the pin depends on various factors, such as shape, material, dielectric index of the surrounding medium, and wavelength.
  • the aspect ratio of a cylinder is the ratio of the height of the cylinder to the diameter of the cylinder.
  • the aspect ratio of a rectangular pin is the ratio of the height of the pin to the width of the pin.
  • the aspect ration is the ratio of the length of the major axis to the length of the minor axis.

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Optical Head (AREA)

Abstract

L'invention concerne un transducteur optique comprenant des moyens (40) conçus pour diriger une onde électromagnétique vers une région focale et une nanostructure (44) métallique présentant un axe longitudinal sensiblement parallèle à un champ électrique de l'onde électromagnétique, ladite nanostructure métallique étant positionnée à l'extérieur des moyens de direction de l'onde électromagnétique. Ladite onde électromagnétique produit des plasmons sur la nanostructure métallique. Un matériau (304, 306) de gaine présente un indice de réfraction différent de l'indice de réfraction des moyens de direction de l'onde électromagnétique et peut être positionnée de manière adjacente à une surface de ladite nanostructure. Des têtes d'enregistrement magnéto-optiques comprennent les transducteurs et des commandes de disques comprennent les têtes d'enregistrement magnéto-optiques.
PCT/US2003/032324 2003-10-10 2003-10-10 Transducteurs optiques a champ proche pour stocker des donnees optiques et magnetiques assiste thermiquement Ceased WO2005045815A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
AU2003284100A AU2003284100A1 (en) 2003-10-10 2003-10-10 Near-field optical transducers for thermal assisted magnetic and optical data storage
PCT/US2003/032324 WO2005045815A1 (fr) 2003-10-10 2003-10-10 Transducteurs optiques a champ proche pour stocker des donnees optiques et magnetiques assiste thermiquement

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FR2921192A1 (fr) * 2007-09-17 2009-03-20 Commissariat Energie Atomique Lentille a immersion solide et procede de realisation associe
WO2010106283A1 (fr) 2009-03-17 2010-09-23 Commissariat A L'energie Atomique Et Aux Energies Alternatives Tete de lecture haute resolution pour disque optique
US8200054B1 (en) 2009-04-19 2012-06-12 Western Digital (Fremont), Llc High efficiency grating coupling for light delivery in EAMR
US8440147B2 (en) 2008-12-30 2013-05-14 Biosurfit, S.A. Analytical rotors and methods for analysis of biological fluids
US8865005B2 (en) 2008-10-23 2014-10-21 Biosurfit, S.A. Jet deflection device
US8916112B2 (en) 2010-03-29 2014-12-23 Biosurfit, S.A. Liquid distribution and metering
US9013704B2 (en) 2009-12-22 2015-04-21 Biosurfit, S.A. Surface plasmon resonance detection system
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Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2921192A1 (fr) * 2007-09-17 2009-03-20 Commissariat Energie Atomique Lentille a immersion solide et procede de realisation associe
WO2009037249A1 (fr) * 2007-09-17 2009-03-26 Commissariat A L'energie Atomique Lentille a immersion solide et procede de realisation associe
US7940477B2 (en) 2007-09-17 2011-05-10 Commissariat A L'energie Atomique Et Aux Energies Alternatives Solid immersion lens and related method for making same
US8865005B2 (en) 2008-10-23 2014-10-21 Biosurfit, S.A. Jet deflection device
US8440147B2 (en) 2008-12-30 2013-05-14 Biosurfit, S.A. Analytical rotors and methods for analysis of biological fluids
WO2010106283A1 (fr) 2009-03-17 2010-09-23 Commissariat A L'energie Atomique Et Aux Energies Alternatives Tete de lecture haute resolution pour disque optique
FR2943450A1 (fr) * 2009-03-17 2010-09-24 Commissariat Energie Atomique Tete de lecture haute resolution pour disque optique
US8200054B1 (en) 2009-04-19 2012-06-12 Western Digital (Fremont), Llc High efficiency grating coupling for light delivery in EAMR
US9013704B2 (en) 2009-12-22 2015-04-21 Biosurfit, S.A. Surface plasmon resonance detection system
US8916112B2 (en) 2010-03-29 2014-12-23 Biosurfit, S.A. Liquid distribution and metering
US9933348B2 (en) 2011-12-08 2018-04-03 Biosurfit, S.A. Sequential aliqoting and determination of an indicator of sedimentation rate

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